This disclosure relates to integrated circuit fabrication.
As integrated circuit (IC) fabrication technique advances, semiconductor manufacturers continue to develop techniques to construct integrated circuits with structures having dimensions in the sub-micron range on a semiconductor substrate. Improvements in photolithographic processing techniques have substantially contributed to the miniaturization of active semiconductor devices to dimensions below a single micron. The fabrication of these semiconductor devices often involves the transfer of circuit patterns from a photolithographic mask or reticle onto a photoresist layer. The process uses an imaging lens apparatus.
The reticle is often itself constructed from a substrate of silicon dioxide. The reticle can be patterned with areas of differing transmissivity thereon. The patterned areas of the reticle represent either the positive or negative images of an integrated circuit structure. After being properly positioned and aligned over the semiconductor wafer, the reticle is subjected to electromagnetic radiation. The radiation passes through transparent portions of the reticle, striking portions of the photoresist layer on the wafer. The resist coating is developed and etched so as to impart a positive or negative image of the reticle pattern onto the photoresist layer remaining on the wafer.
Conventional photolithographic methods of fabricating integrated circuits on a substrate often involve stepping a reticle and imaging apparatus across a photoresist coated wafer. The methods also involve repeatedly transferring the reticle image pattern to adjacent areas on the wafer. Each of the individual areas on the wafer containing the circuitry image is termed a die. The wafer is cut or otherwise segmented at the end of the fabrication process so that the dice are separated from one another for subsequent packaging as individual integrated circuit chips.
As integrated circuits become increasingly complex, however, the integrated circuit structures within an individual die have become significantly smaller and denser. Larger reticles are often required to transfer larger and more complex circuit images to substrate fields of increased dimensions. Because of inherent image resolution limitations associated with conventional photolithographic processes, imaging and alignment errors are often introduced when fine line structures having sub-micron dimensions are produced on relatively large reticles. Further, steppers used in photolithographic process also set the limit on the size of the printed circuit.
The inherent limitations associated with producing relatively large reticles having structures with sub-micron dimensions have motivated development of different types of integrated circuits (IC) with larger fields. One type of circuit includes a plurality of circuit blocks formed on a semiconductor substrate. The circuit blocks are stitched together by appropriately connecting input and output lines of the plurality of circuit blocks. The circuit also includes connecting circuits coupled to the plurality of circuit blocks. The connecting circuits provide low voltage drop across boundaries where the plurality of circuit blocks are stitched together.